Ferrite compositions and method of manufacture



Dec. 28, 1965 FERRITE Filed July 31, 1962 F. R. MONFORTE ET ALCOMPOSITIONS AND METHOD OF MANUFACTURE 2 Sheets-Sheet 2 IN GAUSSMAGNET/C INDUCTION l I l l l l MAGNET/C INDUCTION IN GAUSS -o.5o o.25 0+0.25 +0.50 +|.o F/ELD STRENGTH (H) M/ 05/25 7503 -O.50 -O.25 0 +0.25+0.50 FIELD STRENGTH (H) /N OERSTEDS VENTORS F. R. MONFORTE 8V F. J.SCH/VETTLEIQ ATTORNEY United States Patent ()fiice 3,226,327 PatentedDec. 28, 1965 3,226,327 FERRITE COMPOSITIONS AND METHOD OF MANUFACTUREFrank R. Monforte, Passaic Township, Morris County, and Frank J.Schnettler, Morristown, N.J., assignors to Bell Telephone Laboratories,Incorporated, New York, N.Y., a corporation of New York Filed July 31,1962, Ser. No. 213,639 7 Claims. (Cl. 252-625) This invention relates toa method for making ferrite materials having a substantially rectangularhysteresis loop characteristic and low coercive force, and further tothe materials so produced.

Ferrite materials having substantially rectangular hysteresis loops andlow coercive forces are well known in the art and advantageouslyutilized in magnetic memory devices such as that described in an articleby J. A. Rajchman in the October 1953 Proceedings of the Institute ofRadio Engineers, Volume 41 No. 10, pages 1407- 1421, entitled A MyriabitMagnetic Core Matrix Memory Element.

United States Patent 2,715,109 issued August 9, 1955, toAlbers-Schoenberg, describes a MnO-MgOFe O ferrite system exhibitingparticularly desirable hysteresis loop and coercive forcecharacteristics. This system encompasses the compositional range of 5 to60 mol percent MnO, 8 to 50 mol percent MgO, and 25 to 50 mol percent FeO A lowering in the coercive force exhibited by these compositions,particularly over the compositional range 4-67 mol percent MnO, 8-55 molpercent MgO, and 25-475 mol percent Fe O is realized with zinc oxideadditions of up to 8 percent by weight of composition, in accordancewith United States Patent 2,981,689, issued April 25, 1961 toAlbers-Schoenberg. Additions above 8 percent are strictly avoided due tothe adverse effect of the zinc oxide additions on the hysteresis loopcharacteristic of the ferrite system.

As discussed in these patents, calcium oxide additions to thesecompositions over the restricted range of 0.5 to 5.0 percent by weightof composition act to further lower coercive force without significantlydetracting from the rectangularity of the hysteresis loop. Additions ofat least 0.5 percent are required to noticeably lower coercive force,while additions above 5.0 percent sufficiently detract from therectangular hysteresis loop characteristic so as to preclude their use.

In accordance with the instant invention, it has been determined thatcalcium inclusions in the above-identified magnesium-manganese ferritecompositions in amounts smaller than heretofore utilized by the artresult in significantly lower coercive force values when the calcium isadded by the method of the invention.

More particularly, it has been found that the introduction of calciumduring the ferrite-forming process in the form of a soluble salt havinga solubility with respect to calcium of at least one gram of calcium per100 cc. of water permits the attaining or minimum coercive force valueswhile maintaining rectangularity of the hysteresis loop. A low coerciveforce, rectangular hysteresis loop composition result from calciumadditions made by this method over the calcium inclusion range of 0.075to 0.30 percent by weight of the composition.

A more complete understanding of the invention may be gained from thefollowing description in conjunction with the accompanying drawing, inwhich:

FIG. 1 is a graph on coordinates of coercive force in oersteds againstweight percent calcium showing the coercive force of two identicalferrite compositions containing varying amounts of calcium, the calciumbeing added as a carbonate to the composition depicted by curve 1 and asa soluble salt to the composition depicted by curve 2;

FIGS. 2 through 4 are graphs on coordinates of magnetic induction B ingauss against field strength H in oersteds, showing reproductions of theactual pictures of hysteresis loops as traced on the screen of anoscilloscope of three identical ferrite compositions containing varyingamounts of calcium added to the compositions during processing as asoluble salt, the ferrites being fired at a temperature of 1300 C. for 7/2 hours; and

FIG. 5 is a graph on coordinates of magnetic induction B in gaussagainst field strength H in oersteds, showing a reproduction of anactual picture of a hysteresis loop as traced on the screen of anoscilloscope of a MgO-MnO-ZnOFe O ferrite composition containing 0.2percent by weight calcium added to the ferrite as a soluble salt, theferrite being fired at a temperature of 1250 C. for 10 hours.

Referring more particularly to FIG. 1, depicted curve 1 shows therelationship between coercive force and calcium content of MnO-MgO-Fe Oferrite composition in which the calcium was added as calcium carbonate.This curve is substantially identical to the one resulting when calciumis added as calcium oxide. Commensurate with the art, for example UnitedStates Patent 2,715,109, calcium heretofore has been utilized in theferrite-forming process as either the oxide or carbonate.

Curve 2 of FIG. 1 depicts the relationship between coercive force andcalcium content of the same composition as curve 1. However, inaccordance with the invention, calcium was added as a soluble salt, inthis instance calcium acetate. This curve is exemplary of other solublecalcium salts, such as calcium benzoate, having a solubility withrespect to calcium of at least one gram of calcium per cc. of water.

The significant decrease in coercive force realized by calcium additionsin the form of soluble salts is illustrated by a comparison of curves 1and 2. As shown by curve 2, calcium additions in the form of solublesalts result, for 0.1 percent calcium, in a decrease in coercive forcefrom 1.04 to 0.67 oersteds. Increasingly larger additions result in acorrespondingly sharp decrease in coercive force until, for example, acoercive force of 0.22 5 oersted is achieved for calcium additions of0.25 percent by Weight. Although not plotted, further decreases incoercive force result from even larger additions.

In contrast, as shown by curve 1, calcium additions in the form ofoxides or carbonates result, for 0.1 percent calcium, in a decrease incoercive force from 1.04 oersteds to 0.775 oersted. Thereafter, furthercalcium additions cause the coercive force to increase to an essentiallystable value of 1.0 to 1.04 oersteds over the calcium inclusive range of0.25 to 0.72 percent by weight of composition. A decrease to 0.71oersted is then experienced over the calcium inclusion range of 0.8 to1.0 percent. Although not plotted, further calcium additions up to 1.6percent decrease the coercive force to 0.65 oersted.

Both ferrite compositions depicted by curves 1 and 2 of FIG. 1 have thesame basic ferrite composition: 32.1 mol percent magnesium oxide, 25 molpercent manganese oxide, and 42.9 mol percent ferric oxide. Bothcompositions Were processed under identical conditions including a finalfiring at 1300 C. for 12.5 hours. The data exemplified by curves 1 and 2of FIG. 1 is exemplary of all magnesium-manganese ferrite compositionsdisclosed in United States Patents 2,715,109 and 2,981,689.

FIGS. 2 through 4 show the hysteresis loops associated with a 32.1 molpercent magnesium oxide, 25 mol per cent manganese oxide, and 42.9 molpercent ferric oxide ferrite composition containing 0, 0.1, and 0.25percent by weight calcium, respectively, the calcium being added to thecomposition during processing as calcium acetate. The 0.1 percentcalcium-containing composition, in common with the calcium-freecompositions, exhibits good rectangul-arity and sharp corners. The 0.25percent calcium-containing composition, while also exhibiting goodrectangul-arity, has somewhat rounded corners. Although not shown in thefigures, it has been found that the corners of the hysteresis loops ofcompositions containing an amount of calcium in excess of 0.30 percentare too rounded to satisfy the requirements of a rectangular loopferrite.

Commensurate with the dual objectives of forming a low coercive force,rectangular hysteresis loop ferrite composition, the data discussed inconjuction with the figures dictates a calcium content for thepreviously described ferrite compositions of 0.075 to 0.30 percentcalcium by weight of the composition. Calcium inclusions greater than0.30 percent adversely affect the rectangularity of the hysteresis loop,with inclusions less than 0.075 percent being too small to sufficientlyminimize coercive force. Based on these considerations, a preferredcalcium content range is 0.13 to 0.30 percent by weight, with an optimumrange being 0.20 to 0.25 percent.

FIG. 5 shows the hysteresis loop associated with a 20 mol percentmagnesium oxide, 23.1 mol percent manganese oxide, 39.5 mol percentferric oxide, and 17.4 mol percent zinc oxide ferrite compositioncontaining 0.2 percent by weight calcium. As shown, the zinc-containingcomposition exhibits good rectangularity and the corners of the curve,while being somewhat rounded, are sufficiently sharp to satisfy therequirements of a rectangular hysteresis loop ferrite. Zinc oxideadditions in excess of 18 mol percent sufficiently detract from therectangularity of the loop as to preclude their inclusion in themagnesium-manganese ferrite compositions disclosed in United StatesPatents 2,715,109 and 2,981,689.

As evidenced by FIG. 5, therefore, the calcium-containing compositionsof the invention permit the beneficial inclusion of zinc oxide inamounts up to 18 mol percent (14 percent by weight of composition). Incontrast, United States Patent 2,981,689 precludes such additions inamounts greater than 8 percent by weight due to their adverse effect onthe rectangularity of the loop.

With the exception that calcium is initially present as a soluble salt,the ferrite-forming process of the invention is otherwise conventionaland, as such understood by the art. Commensurate with the art, suchprocessing includes forming a slurry of the desired components, thecomponents being present as the oxides or other compounds which, withfiring, will yield the oxides. The slurry also contains calcium presentas a soluble salt having a solubility with respect to calcium of atleast one gram of calcium per 100 cc. of water. Since the amount ofwater necessary to form the slurry is sufficient to dissolve the salt,the salt may be introduced to the slurry mixture as either the salt perse or a solution of the salt in water.

After mixing the components, the slurry is dried, resulting in a finedispersion of the calcium salt throughout the mixture. The mixture isthen calcined, which causes the salt to decompose, leaving calcium oxidefinely dispersed throughout the calcined mixture. In accordance withaccepted practice, an illustrative calcining example would compriseheating the mixture over an appropriate temperature range of 800 C. to1100 C. for 2 to 16 hours.

The agglomerations formed during calcining are broken up by ballmilling, generally for a period of 5 to hours, in a carrier such aswater, acetone, ethanol, or carbon tetrachloride. Typically, a binder isadded during ball milling to aid in properly binding the compositiontogether. Although not so limited, conventional binders includepolyvinyl alcohol or Opal Wax (hydrogenated castor oil) for a watercarrier and parafiin or Hal-owax (chlorinated naphthalene) for organiccarriers.

The ball-milled slurry is then dried and the resulting solids granulatedinto particles of nearly uniform size. Generally, a 10 or #20 UnitedStates standard mesh is used for this purpose. The particles are thenformed into the desired configuration under pressures in the order of5,000 to 50,000 pounds per square inch. Final firing of the shaped bodycompletes formation of the ferrite com-position. Such firing involvesheating at temperatures preferably in the order of 1200 C. to 1350 C.for several hours, for example 7 to 15 hours. The firing is generallycarried out in an oxygen-containing atmosphere, the fired product beingthen cooled to room temperature in an inert atmosphere such as nitrogen.

It is understood that the preceding outline of one method for preparingferrite articles is to be construed as illustrative only, other methodsbeing readily apparent to those skilled in the art. The only criticalprocessing step differing from that conventionally utilized by the artis the addition of calcium as the previously discussed soluble salt tothe mixture of desired components before the calcining step.

The following specific examples are given by way of illustration, andare not to be construed as limiting in any way the scope and spirit ofthe invention.

Example 1 54.7 grams magnesium carbonate, 58.0 grams manganesecarbonate, 138.1 grams ferric oxide, and 0.79 gram calcium acetate weredry mixed. The mixed ingredients were funneled into an EppenbachHomo-Mixer and enough distilled water was added thereto to form aslurry. The slurry was then dried in a heated planetary mixer. The dryfilter cake thus obtained was then calcined in air at a temperature of900 C. for 16 hours. After calcining, the mixture was ball-milled incarbon tetrachloride for 16 hours. A ten percent by weight addition ofHalowax to serve as a binder was introduced during ball milling. Afterball milling, the solvent was substantially removed by drying themixture in a heated planetary mixer. The material was then granulated bypassing it through a #20 United States standard screen mesh and thenfurther dried for six hours in a vacuum at a temperature of 45 C. toremove the last traces of the solvent. The material was then shaped intoa ring having the dimensions 0.50 inch OD. and 0.35 inch I.D. under apressure of 50,000 pounds per square inch. After shaping, the ring wasdewaxed by bringing it to a temperature of 400 C. over a period of sixhours and maintaining the 400 C. temperature for another six hours. Thefinal firing of the ring was carried out in an oxygen atmosphere at atemperature of 1300 C. for 7.5 hours. The ring was then allowed to coolto room temperature in a nitrogen atmosphere.

The formed ring had the composition of 32.1 mol percent magnesium oxide,25 mol percent manganese oxide, 42.9 mol percent ferric oxide, and 0.1percent calcium by weight of the composition. The ring had thehysteresis loop depicted by FIG. 3 of the drawing and a coercive forceof 0.67 oersted.

Example 2 54.7 grams magnesium carbonate, 58.0 grams manganesecarbonate, and 138.1 grams ferric oxide were dry mixed. The mixedingredients were funneled into an Eppenbach Homo-Mixer and enoughdistilled Water was added thereto to form a slurry. milliliters ofcalcium acetate solution containing 1.97 grams of calcium acetate wasthen added to the slurry, which then underwent the same processing stepsdescribed in conjunction with Example 1.

The formed ring had the composition: 32.1 mol percent magnesium oxide,25 mol percent manganese oxide, 42.9 mol percent ferric oxide, and 0.25percent by weight calcium. The ring had the hysteresis loop depicted byExample 3 33.2 grams magnesium carbonate, 52.2 grams manganesecarbonate, 124.1 grams ferric oxide, 27.9 grams zinc oxide, and 1.58grams calcium acetate were dry mixed. The mixture then underwent thesame processing steps described in conjunction with Example 1.

The formed ring had the composition: mol percent magnesium oxide, 23.1mol percent manganese oxide, 39.5 mol percent ferric oxide, 17.4 molpercent zinc oxide, and 0.2 percent by Weight calcium. The ring had thehysteresis loop depicted by FIG. 5 of the drawing and a coercive forceof 0.13 oersted.

What is claimed is:

1. A method of making a rectangular hysteresis loop ferrite compositioncomprising the steps of slurrying with water, drying, and calcining amixture comprising components equivalent to 5 to 60 mol percentmanganese oxide, 8 to 50 mol perecnt magnesium oxide, to mol percentferric oxide, and containing from 0.075 to 0.30 percent calcium byWeight of the mixture added as a soluble salt having a solubility withrespect to calcium of at least one gram of calcium per 100 cc. of Water,shaping the resultant material under pressure into the desiredconfiguration, and firing the shaped material at a temperature of from1200 C. to 1350 C., the said soluble salt being of such nature as toyield calcium oxide during the said method.

2. The method in accordance with claim 1 wherein said mixture containsfrom 0.13 to 0.30 percent calcium added as calcium acetate.

3. The method in accordance with claim 2 wherein said mixture containsfrom 0.20 to 0.25 percent calcium.

4. A method of making a rectangular hysteresis loop MnO 4 to 67 MgO 8 toFe O 25 to 47.5 ZnO 0 to 18 and from 0.075 to 0.30 percent calcium byweight of the mixture added as a soluble salt having a solubility withrespect to calcium of at least one gram of calcium per cc. of Water,shaping the resultant material into the desired configuration under apressure of 5,000 to 50,000 pounds per square inch, and firing theshaped material at a temperature of from 1200 C. to 1350 C., the saidsoluble salt being of such nature as to yield calcium oxide during thesaid method.

5. The method in accordance with claim 4 wherein said mixture containsfrom 0.13 to 0.30 percent calcium added as calcium acetate.

6. The method in accordance with claim 5 wherein said mixture containsfrom 0.20 to 0.25 percent calcium.

7. Product produced by the method of claim 1.

References Cited by the Examiner UNITED STATES PATENTS 2,903,429 9/1959Guillaud 25262.5 2,981,689 4/1961 Albers-Schoenberg 25262.5

FOREIGN PATENTS 1,174,680 11/1958 France.

TOBIAS E. LEVOW, Primary Examiner.

MAURICE A. BRINDISI, Examiner.

1. A METHOD OF MAKING A RECTANGULAR HYSTERESIS LOOP FERRITE COMPOSITIONCOMPRISING THE STEPS OF SLURRYING WITH WATER, DRYING, AND CALCINING AMIXTURE COMPRISING COMPONENTS EQUIVALENT TO 5 TO 60 MOL PERCENTMANGANESE OXIDE, 8 TO 50 MOL PERCENT MAGNESIUM OXIDE, 25 TO 50 MOLPERCENT FERRIC OXIDE, AND CONTAINING FROM 0.075 TO 0.30 PERCENT CALCIUMBY WEIGHT OF THE MIXTURE ADDED AS A SOLUBLE SALT HAVING A SOLUBILITYWITH RESPECT TO CALCIUM OF AT LEAST ONE GRAM OF CALCIUM PER 100 CC. OFWATER, SHAPING THE RESULTANT MATERIAL UNDER PRESSURE INTO THE DESIREDCONFIGURATION, AND FIRING THE SHAPED MATERIAL AT A TEMPERATURE OF FROM1200*C. TO 1350*C., THE SAID SOLUBLE SALT BEING OF SUCH NATURE AS TOYIELD CALCIUM OXIDE DURING THE SAID METHOD.
 7. PRODUCT PRODUCED BY THEMETHOD OF CLAIM 1.